1. Field of the Invention
Exemplary embodiments of the invention relate to the art of power steering devices and, more particularly, to a power steering device having a compliant gear.
2. Description of Background
Electric Power Steering (“EPS”) has been the subject of development by auto manufacturers and suppliers for well over a decade due in part to potential advantages of fuel economy and ease-of-control when compared with traditional hydraulic power steering (“HPS”). However, commercialization of EPS systems has been slow and is presently limited due to cost and performance challenges. Among the most challenging technical issues are a pulsating feel at the steering wheel and an audible noise associated with the type of high performance electric drives needed to meet steering requirements.
Current EPS systems experience rattle issues associated with motor inertia. Increased motor inertia causes high torque reversals along an intermediate shaft portion of the EPS when driving over bumps and the like. The high torque reversals give rise to rattles at various locations within the EPS system. Rattles develop in such locations as, worm-to-worm gear, EPS motor bearings, EPS motor-to-worm coupling, intermediate shaft cardan joints, rack-to-pinion teeth, rack-to-bushing, rack-yoke-to-housing and the like.
In order to reduce rattles, manufactures have added compliance to various components of the EPS. However, while compliant components can reduce unwanted noise, the compliant components often detract from steering “feel”. Adding compliance to a steering shaft, for example, will certainly reduce unwanted noise, but will also provide a very soft steering “feel”. In order to provide good steering “feel” and minimize unwanted noise, manufactures have added torsional and radial compliance to EPS worm and worm gear set. Unfortunately, when adding compliance to one or more worm gears, worm-worm alignment is affected. That is, the compliance creates a shifting of an axial alignment between the worm and the worm gear. In many cases, the shifting has no effect on steering. In other cases, axial alignment between components is important. For example, when using an enveloping worm gear, axial misalignment is not acceptable. Misalignment between enveloping worm gears can create binding and excessive component wear.